Method of forming and cooling pinhole spatial filter for high power laser

ABSTRACT

An electrostatically cooled spatial filter for high powered pulsed lasers wherein the filter comprises a first lens which focuses a laser beam on a pinhole, and a second lens positioned behind the pinhole to receive the beam. To prevent the laser beam from destroying the pinhole an electric field is applied across the pinhole. This field cools the pinhole and as a result the size of the pinhole is preserved.

XR snzewao I i United States Patent [191 [1 1 3,724,930 Farmer [4 Apr. 3, 1973 [54] METHOD OF FORMING AND [56] References Cited COOLING PINHOLE SPATIAL FILTER FOR HIGH POWER LASER UNITED STATES PATENTS 3 415 5 7 [75] Invent wimm Fame" 314511725 2323 et al.... .3 5 6 /1 0; Tenth 3,224,497 12/1965 Blomgren et al. ..62/3 x Assigneez of as Chen rqpresemed by the Secretary of the Primary ExaminerDavid H. Rubin Force Att0meyHarry A. Herbert et al. [22] Filed: July 21, 1972 [21] Appl. No.: 274,031 [57] ABSTRACT v An electrostatically cooled spatial filter for high Related Appllcatlon Data powered pulsed lasers wherein the filter comprises a [62] Division of 96,819, Dec. 10 1970 first lens which focuses a laser beam on a pinhole, and a second lens positioned behind the pinhole to receive the beam. To prevent the laser beam from destroying :L'f' 350/320 62/3 the pinhole an electric field is applied across the pin- 58 d 94 62 hole. This field cools the pinhole and as a result the 1 0 can l l' size of the pinhole is preserved.

1 Claim, 1 Drawing Figure l2 K V SouRcE m H/GH POWER PUL SED LASER METHOD OF FORMING AND COOLING PINHOLE SPATIAL FILTER FOR HIGH POWER LASER This is a division of application Ser. No. 96,819 filed Dec. 10, 1970, entitled Electrostatic Spatial Filter For A High Power laser, by William M. Farmer.

This invention relates to a filter for a laser, and more particularly, to an electrostatically cooled spatial filter for a high power pulsed laser.

A commonly used device on lower power CW lasers is a pinhole spatial filter and beam expander. The reason for using such a device is to eliminate the degrading effects of dust and scratches on the optical elements in the laser system and lenses. Physically, the spatial filter consists of a small positive lens which focuses the laser beam to a small hole, 10 pm-25 pm in diameter; the expanded laser beam is then collimated with a second lens to produce an enlarged beam of spatially filtered light. U. S. Pat. Nos. 3,415,587 and 3,451,755 both disclose the use of spatial filters with a laser beam. However, these filters are of the conventional type and do not include an electric field across the pinhole.

I-Ieretofore, it has been impossible to use such a device with high powered pulsed lasers due to the fact SUMMARY OF THE INVENTION An electrostatically cooled spatial filter for high power pulsed lasers is provided. The spatial filter is comprised of a small positive lens which focuses the laser beam to a small hole such as a pinhole. The expanded laser beam is then collimated with a second lens to produce an enlarged beam of spatially filter light. By using the proper material for the pinhole, high electric fields are utilized to cool the pinhole and keep the laser from destroying it. The material found most useful for this purpose is aluminum (Al) foil.

An object of this invention is to provide an electrostatically cooled spatial filter for high powered pulsed lasers.

Another object of this invention is to provide a pinhole spatial filter of lasers in which high electric fields are utilized to cool the pinhole.

Yet another object of this invention is to provide a pinhole spatial filter for lasers in which the pinhole is made by pulsing the lasers and producing a pinhole in a metal material with no applied potential and thereafter applying a potential to create a high electric field across the pinhole.

DESCRIPTION OF DRAWING A single FIGURE is shown illustrating the preferred embodiment of the electrostatically cooled spatial filter for a high power pulsed laser.

DESCRIPTION OF PREFERRED EMBODIMENT Now referring in detail to the single FIGURE of the present invention, there is shown conventional high power pulsed laser 1. Cylindrical tube 2 having ends 3 and 4 are provided. Positive lens 5 and positive lens 6 are pressure fitted into ends 3 and 4 respectively. Metal material such as aluminum foil is positioned inside of cylindrical tube 2 by member 7a and it becomes pmhole 7. Twelve kilovolt source 8 has connected thereto needle probe 9. Needle probe 9 includes needle 10. Needle probe 9 is also pressure fitted into cylindrical tube 2 in such fashion as to place needle 10 in any desired position. Metal plate 11 is fixed in position by rigid metal wire 12 which is affixed to cylindrical tube 2. Metal wire 12 is connected to ground by way of line 13.

In the operation of the preferred embodiment, small positive lens 5 focuses the laser output from high powered pulsed laser to a small hole in pinhole 7. The expanded laser beam is then collimated with positive lens 6 to produce an enlarged beam of spatially filtered light. Simultaneously, a 12 kilovolt potential is applied to needle probe 9 and needle 10. Plate 11 is ground with respect to the probe thereby providing high electric fields to cool pinhole 7 and keep the laser from destroying it.

It is noted that the spatial filter is made by pulsing the laser and producing a pinhole with no applied potential. Thereafter, the potential is applied and the initial pinhole size preserved.

With this method of spatially filtering high power pulsed laser beams, collimated beams of light of high intensity and spatial purity may be produced. Such beams will enhance the quality of holograms requiring pulsed laser light for formation and should simplify many holographic procedures used heretofore.

What is claimed is:

1. In the combination of a high power pulsed laser with a pinhole spatial filter, the method of forming through metal a pinhole having an optimum dimension and the preservation of the optimum dimension during operation of the combination comprising passing high powered output pulses from said high power pulsed laser through said pinhole spatial filter only until forming a pinhole in said metal, the formed pinhole then being of optimum dimension for said combination, and immediately thereafter establishing exclusively an electrostatic field across the formed pinhole for cooling thereof to obtain said preservation of said optimum dimension during subsequent operation of said combination, said electrostatic field existing on either side of said pinhole and also therethrough without interfering with the passage of the output pulses from said high power pulsed laser. 

1. In the combination of a high power pulsed laser with a pinhole spatial filter, the method of forming through metal a pinhole having an optimum dimension and the preservation of the optimum dimension during operation of the combination comprising passing high powered output pulses from said high power pulsed laser through said pinhole spatial filter only until forming a pinhole in said metal, the formed pinhole then being of optimum dimension for said combination, and immediately thereafter establishing exclusively an electrostatic field across the formed pinhole for cooling thereof to obtain said preservation of said optimum dimension during subsequent operation of said combination, said electrostatic field existing on either side of said pinhole and also therethrough without interfering with the passage of the output pulses from said high power pulsed laser. 